Project Summary Relapse to drug use even after extended periods of abstinence is a major obstacle in the rehabilitation of cocaine users. In rodents, experiments have consistently demonstrated that drug-seeking behavior, such as responding for cocaine-associated cues, progressively increases following abstinence from cocaine. A better understanding of the circuitry that underlies these abstinence-induced increases in drug-seeking behavior will be critical in developing hypothesis-driven therapeutic strategies for the prevention of relapse. Given the loss of control often observed in addiction, the prefrontal cortex, which exerts ?top-down? control on many downstream structures, has received a great deal of attention. However this region is highly heterogeneous, composed of many different neuronal subpopulations each with distinct patterns of afferent and efferent projections. To date, it has been difficult to ascertain what information is being encoded by projection-defined subpopulations during drug-seeking behavior, as well as how these populations contribute causally to increased drug-seeking following abstinence. The subpopulation of infralimbic (IL) neurons that project to the nucleus accumbens (NAc) is of particular interest, given the role of both of these structures in increased drug-seeking following abstinence. The proposed NRSA research plan will clarify the contribution of NAc-projecting IL neurons to increased cocaine-seeking behavior following abstinence by recording and manipulating activity specifically in this subpopulation of neurons. Specific Aim 1 will use cellular resolution calcium imaging to identify neural correlates of IL?NAc projecting neurons in rats during an extinction session to assess cue-induced cocaine- seeking. Behavior and neural correlates will be compared between rats before and after cocaine abstinence. Specific Aim 2 will use optogentics to examine the causal contribution of the IL?NAc projection to increased cocaine-seeking following abstinence. Rats will be trained to self-administer cocaine, and IL?NAc neurons will be optogenetically activated on a subset of trials during an extinction session to test cue-induced drug-seeking before or after prolonged abstinence. Drug-seeking will be compared between trials in which this pathway is activated versus trials in which it is not. By combining correlational and causal techniques, this research has the potential to provide novel insights for the development of relapse prevention therapies in clinical populations.